Fuse structure

ABSTRACT

A fuse structure is described. The fuse structure includes a first region adapted to be coupled to a voltage source, a second region adapted to be coupled to a ground, and a current flow region disposed between the first and second regions. The current flow region has a configuration that causes a void to be opened at a point of localized heating due to current crowding within the current flow region and that causes the void to propagate across the current flow region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending application patentapplication, Ser. No. 10/621,484, entitled “A Fuse Structure,” filedJul. 16, 2003, and assigned to the assignee of the present invention,the disclosure of which is hereby incorporated by reference.

BACKGROUND

Fuses, or more specifically micro fuses, can be used to encode (store)information in devices such as removable printer components (e.g., inkcartridges) used in printer systems. For example, a device can include anumber of fuses. A blown fuse has a higher, or substantiallyopen-circuit, resistance, while a non-blown fuse has a lower, orsubstantially closed-circuit, resistance. Information can be encodeddepending on which fuses are blown or the particular combination ofblown fuses. In a printer system, the type of information encoded mayinclude, for example, identification of the type of product, the amountof ink provided by an ink cartridge, and the value of a thermal senseresistor associated with the ink cartridge.

The fuses may be blown during the manufacturing process or afterwards.Oftentimes there is difficulty in reliably blowing the fuses on aconsistent basis. Variability in manufacture can result in some fusesblowing at a given voltage while others will not. This can result insome fuses that are intended to exhibit a substantially open-circuitresistance exhibiting a substantially closed-circuit resistance instead.Fuses can also “under blow,” meaning that they are partially but notcompletely blown. A higher voltage can be used to help ensure that theappropriate fuses will reliably blow. However, too much voltage cancause fuses to “over blow,” meaning that they blow too vigorously,perhaps causing damage to other layers of the fuse structure.

Variability in temperature from one fuse to another is another factorthat contributes to the difficulty in blowing fuses reliably andconsistently.

Not only do the factors described above combine to increase theuncertainty that a fuse can be blown, but they also introduceuncertainty into the fuse-blowing process. For example, it can be moredifficult to identify beforehand what voltage should be used to blow theappropriate fuses.

For these and other reasons, there is a need for the present invention.

SUMMARY OF THE INVENTION

Embodiments of the present invention pertain to a fuse structure, to abus that can be coupled to the fuse structure, and to a combination ofthese elements. The fuse structure includes a first region adapted to becoupled to a voltage source, a second region adapted to be coupled to aground, and a current flow region disposed between the first and secondregions. The current flow region has a configuration that causes a voidto be opened at a point of localized heating due to current crowdingwithin the current flow region and that causes the void to propagateacross the current flow region.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention.

FIG. 1 is a cross-sectional view showing certain layers used in forminga fuse structure according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a fuse structure formedaccording to one embodiment of the present invention.

FIG. 3 illustrates an embodiment of a fuse structure in accordance withthe present invention.

FIG. 4 illustrates a void propagating across the fuse structure of FIG.3.

FIG. 5 illustrates another embodiment of a fuse structure in accordancewith the present invention.

FIG. 6 illustrates another embodiment of a fuse structure in accordancewith the present invention.

FIG. 7 illustrates another embodiment of a fuse structure in accordancewith the present invention.

FIG. 8 illustrates one embodiment of a bus in accordance with thepresent invention.

FIG. 9 is a perspective diagram of an exemplary printer system in whichembodiments of the present invention can be implemented.

FIG. 10 is a flowchart of a process for blowing fuses according to oneembodiment of the present invention.

The drawings referred to in this description should be understood as notbeing drawn to scale except if specifically noted.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction withthese embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims. Furthermore, in the following description of thepresent invention, numerous specific details are set forth in order toprovide a thorough understanding of the present invention. In otherinstances, well-known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

FIG. 1 is a cross-sectional view showing certain layers in a stack 30used in forming a fuse structure according to one embodiment of thepresent invention. More specifically, shown are layers that are used toform a metal-1 layer in a micro fuse according to one embodiment of thepresent invention. In the present embodiment, the metal-1 layer actuallyincludes a first (conductive) layer 31 and a second (resistive) layer32. The first layer 31 and the second layer 32 are disposed over anunder layer (or layers) 35.

The first layer 31 includes material that has a lower resistance and thesecond layer 32 includes material that has a higher resistance. In onesuch embodiment, the first layer 31 is made up of aluminum and copper,and the second layer 32 is made up of tantalum and aluminum. Othermaterials can be used. For example, the second layer 32 can be made upof materials including, but not limited to, tantalum nitride,polysilicon, hafnium bromide, and metal silicon nitrides such as WSiN(tungsten silicon nitride).

An etch process such as a slope metal etch process, or some otherprocess for selectively removing material, is applied to the metal-1layer to remove the first layer 31 in the area of the micro fuse (fuseregion 36), exposing the second layer 32 when viewed from above. This isillustrated in cross-sectional view by FIG. 2. Other layers (e.g., overlayer or layers 34) may also be present.

In the absence of the first layer 31 in the area of the micro fuse,current is caused to flow through second layer 32, the layer of higherresistance. Significantly, as will be seen by the discussion of FIGS. 3,4, 5, 6 and 7 below, the second layer 32 forms a current flow regionparticularly configured to cause consistent and reliable blowing offuses when appropriate.

FIG. 3 illustrates a fuse structure 40 in accordance with one embodimentof the present invention. More specifically, illustrated is the currentflow region of a micro fuse. FIG. 3 is a top down view of a metal-1layer in a stack of layers (the other layers are not depicted). The fusestructure is couplable to a voltage source and to a ground (refer alsoto the discussion of FIG. 8, below).

The current flow region of the fuse structure is in the second(resistive) layer 32 in the fuse region 36 of FIG. 2. The current flowregion is asymmetric. That is, the current flow region is asymmetricallyshaped about an axis 47 that is essentially parallel to the generaldirection of current flow from the voltage source to the ground.

In the embodiment of FIG. 3, the current flow region has a configurationthat defines a recess 41 that extends into the current flow region fromone side of the fuse structure 40. In the top down view of FIG. 3, therecess 41 is shown as appearing on one side of fuse structure 40;however, the recess 41 can instead be on the other side. The recess 41is substantially symmetrical about an axis 42 that is orthogonal to thegeneral direction of current flow. In the embodiment of FIG. 3, therecess 41 is essentially triangular in shape.

The recess 41 induces current crowding in the narrowed portion of thecurrent flow region formed by the recess 41. Due to the asymmetricconfiguration of the fuse structure 40, the temperature increase acrossthe narrowed portion of the current flow region will not be uniform.More specifically, the configuration of the current flow region causeslocalized heating at a point 43. The point 43 will therefore be at ahigher temperature than other points located within the narrowed portionof the current flow region. As a result, a void in the resistive layerwill form first at point 43.

Accordingly, a consistent initiation point leading to blowing of thefuse is achieved. In general, the point 43 is likely to be locatedproximate to the point at which recess 41 extends furthest into thecurrent flow region.

FIG. 4 illustrates propagation of a void, opened as described above,across the fuse structure of FIG. 3. With the introduction of a void atpoint 43, current crowding and the attendant localized heating will moveto a point 45 adjacent to the initiation point 43. The void will as aresult expand to include point 45. With the void now extending to point45, current crowding and the attendant localized heating will movefurther to the left (according to the orientation of FIG. 4). In thismanner, the void will continue to propagate across the narrowed portionof the current flow region until it extends all the way across thecurrent flow region, thereby blowing the fuse.

In summary, the asymmetric configuration of the fuse structure causescurrent crowding, which in turn causes the greatest localized heating ata point that is propagated across the current flow region as the void ispropagated across the current flow region. In effect, the configurationof the fuse structure focuses the current crowding at a point. By virtueof this effect, a void in the current flow region can be reliably openedstarting at that point and then propagated, and the fuse can thereforebe reliably blown. Moreover, lower voltages can be used, meaning that ifa fuse should be over blown, the likelihood of damage to surroundinglayers is reduced. Also by virtue of this effect, the voltage needed toopen and propagate a void can be more reliably predicted.

FIG. 5 illustrates another embodiment of a fuse structure 50 inaccordance with the present invention. In this embodiment, theconfiguration of the current flow region defines a recess 51 that issubstantially trapezoidal in shape. The recess 51 is substantiallysymmetrical about an axis 52 that is orthogonal to the general directionof current flow.

The recess 51 has a “flat” portion 53, rather than coming to a point asin the embodiment of FIGS. 3 and 4. The portion 53 creates a region 55of consistent resistance within the current flow region of fusestructure 50. The length L of portion 53 can be varied to achieve adesired resistance characteristic.

FIG. 6 illustrates yet another embodiment of a fuse structure 60 inaccordance with the present invention. In this embodiment, theconfiguration of the current flow region defines a recess 61 that has asubstantially straight side 62. The straight side 62 is on the side ofthe recess 61 closest to the source of the current (that is, side 62 ison the upstream side of recess 61).

FIG. 7 illustrates still another embodiment of a fuse structure inaccordance with the present invention. In this embodiment, theconfiguration of the current flow region defines a recess 71 that has asubstantially straight side 72. The straight side 72 is on the side ofthe recess 71 away from the source of the current (that is, side 72 ison the downstream side of recess 71).

In summary, in each of the embodiments described above, a recess isdefined that extends into the region of current flow within a fuse. Therecess extends from one side of the fuse so that the current flow regionis asymmetrically shaped. The extent to which the recess extends intothe current flow region is a design parameter. In one embodiment, therecess extends more than about half-way across the current flow region.

Although FIGS. 3–7 describe certain configurations that can be used, itis appreciated that the present invention is not so limited. Forexample, a chevron-shaped recess can be defined. Recesses of othershapes that induce localized heating that results in initiation of avoid in the current flow region can be used. Variation in the generalshape of the recess from that described herein is permitted with thisaim in mind. It is also appreciated that combinations of theconfigurations described herein can be used.

FIG. 8 illustrates one embodiment of a bus 80 in accordance with thepresent invention. In the present embodiment, bus 80 is described as apower bus; however, bus 80 can also be a ground bus.

Bus 80 can be coupled to a plurality of circuit elements. In the presentembodiment, bus 80 is coupled to a plurality of circuit elementsexemplified by circuit element 81. The bus 80 can be coupled to thecircuit elements 81 either directly or via multiplexing circuitry. Inone embodiment, the circuit elements are fuses such as those configuredaccording to the embodiments described in conjunction with FIGS. 3–7,although the present invention is not so limited.

Bus 80 of FIG. 8 is coupled to the circuit elements 81 by a plurality offirst segments exemplified by segment 82. A second segment 83 is coupledto each of the first segments 82. The first segments 82 couple thesecond segment 83 to each of the circuit elements 81. The configurationof the bus 80, including the first segments 81 and the second segment82, can be said to resemble a comb.

In one embodiment, the first segments 82 are approximately equal inlength and are substantially parallel to each other, and the secondsegment 83 is substantially orthogonal to the first segments 82.According to such an embodiment, the second segment 83 is essentiallyequidistant from each of the circuit elements 81.

The second segment 83 is separated from the circuit elements 81 by adistance defined by the length of the first segments 82. The length ofthe first segments 82 is a design consideration. The length of the firstsegments 82 is selected to thermally insulate the circuit elements 81from the second segment 83. As such, the second segment 83 will not actas a heat sink for the circuit elements. As a consequence, each of thecircuit elements 81 is heated to approximately the same degree. Thevariability in heating of one fuse versus another is thereby removedfrom the fuse-blowing process, resulting in more consistent and reliablefuse blowing. In another words, using bus 80, each fuse coupled to thebus is subject to essentially the same thermal loads.

Moreover, the second segment 83 is narrow enough to prevent it fromacting as a heat sink. In addition, the third segment 84 of the bus 80is likewise narrow enough to prevent it from acting as a heat sink.Also, the third segment 84 is thermally insulated from the circuitelements 81 by virtue of its distance from those elements, so that thisportion of the bus 80 is further prevented from acting as a heat sink.It is recognized that, by narrowing portions of the bus 80, there is atradeoff between the capacity of the bus to carry current and thecapacity of the bus to serve as a heat sink. In other words, thedimensions of the bus 80 can be selected to achieve a desirable balancebetween the electrical and thermal (e.g., heat sink) characteristics ofthe bus.

FIG. 9 is a perspective diagram (partial cut-away) of an exemplaryprinter system 101 upon which embodiments of the present invention canbe implemented. Exemplary printer system 101 includes a printer housing103 having a platen 105 to which input media 107 (e.g., paper) istransported by mechanisms known in the art. Additionally, exemplaryprinter system 101 includes a carriage 109 holding at least oneremovable printer component 111 (e.g., a printer cartridge) for ejectingfluid such as ink onto input media 107. Carriage 109 is typicallymounted on a slide bar 113 or similar mechanism to allow the carriage109 to be moved along a scan axis, X, denoted by arrow 115. Also, duringtypical operation, input media 107 is moved along a feed axis, Y,denoted by arrow 119. Often, media 107 travels along the feed axis, Y,while ink is ejected along an ink drop trajectory axis, Z, as shown byarrow 117. Exemplary printer system 101 is also well suited to use withreplaceable printer components such as semi-permanent printheadmechanisms having at least one small volume, on-board, ink chamber thatis sporadically replenished from fluidically-coupled, off-axis, inkreservoirs or replaceable printer components having two or more colorsof ink available within the replaceable printer components and inkejecting nozzles specifically designated for each color. Exemplaryprinter system 101 is also well suited to use with replaceable printercomponents of various other types and structures. Although such anexemplary printer system 101 is shown in FIG. 9, embodiments of thepresent invention are well suited to use with various other types ofprinter systems. Embodiments of the present invention can also beutilized in systems other than printer systems.

The fuse design and/or the bus design described above can be used duringthe manufacturing process of the printer system, including each of itsvarious components, or after the manufacturing process. The fuses can beused to store information on the printer system including any of itscomponents, such as the ink cartridge, for example.

FIG. 10 is a flowchart 200 of a process for blowing fuses according toone embodiment of the present invention. Although specific steps aredisclosed in flowchart 200, such steps are exemplary. That is,embodiments of the present invention are well suited to performingvarious other steps or variations of the steps recited in the flowchart.It is appreciated that the steps in the flowchart may be performed in anorder different than presented, and that not all of the steps in theflowchart may be performed.

In step 202, a current is generated in a current flow region of a fusecoupled to a power bus.

In step 204, localized heating is induced at a point in the current flowregion because of the shape of that region. More specifically, thecurrent flow region has a configuration that causes current crowding ata point in the current flow region. Various embodiments of aconfiguration that can cause current crowding and localized heating aredescribed above in conjunction with FIGS. 3–7.

In step 206 of FIG. 10, a void is opened in the current flow region,specifically at the point of current crowding and localized heatingmentioned in step 204.

In step 208, the void is propagated across the current flow regionbecause of the shape of that region. Eventually, the void can propagateentirely across the current flow region, blowing the fuse.

In step 210, when there are several fuses coupled to the power bus, thefuses are each subjected to substantially the same thermal loads becausethe bus is configured and dimensioned so that the bus does not serve asa heat sink for the fuses.

In summary, embodiments of the present invention allow fuses to be blownon a consistent and reliable basis, reducing or eliminating instances inwhich fuses are over blown or under blown. With the improvedreliability, variability in fuse-blowing processes can be reduced. Forexample, with fuse blowing more reliably predicted to occur, anacceptable applied voltage range can be defined with confidence thatvoltages in that range will result in the appropriate fuses being blownon a consistent basis.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and many modifications andvariations may be possible in light of the above teaching. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical application, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

1. A bus configured for use with a removable printer component, the buscomprising: a plurality of elongated, electrically-conductive firstsegments; a plurality of microfuses, one microfuse being provided alongeach of the first segments at least one of the microfuses comprising alaminate comprising a first layer and a second layer, said first layerhaving a lower electrical resistance than said second layer, whereinsaid second layer comprises: a first region adapted to be coupled to avoltage source; a second region adapted to be coupled to a ground; and acurrent flow region disposed between said first and second regions,wherein said current flow region is uncurved between said first andsecond regions and wherein said current flow region defines a recess inthe plane of said second layer, said recess extending from one side ofsaid current flow region into said current flow region, wherein saidrecess extends more than approximately halfway across said current flowregion; an elongated, electrically-conductive second segment from whicheach of the first segments extends; and an elongated,electrically-conductive third segment from which the second segmentextends; wherein the first segments extend from the second segment inthe same direction and are substantially parallel to each other, whereinthe microfuses are spaced from the second segment in a manner in whichthe microfuses are thermally insulated from the second segment, whereinthe second segment is sized and configured to reduce the amount of heatthe second segment can store, and wherein the third segment is sized andconfigured to reduce the amount of heat the third segment can store andis spaced from the microfuses in a manner in which the microfuses arethermally insulated from the third segment.
 2. The bus of claim 1wherein said bus is one of a power bus and a ground bus.
 3. The bus ofclaim 1 wherein said first segments are substantially equal in length.4. The bus of claim 1 wherein said second segment is substantiallyorthogonal to said first segments.